Organic solar cell

ABSTRACT

The present specification relates to an organic solar cell including a first electrode; a second electrode; and one or more organic material layers including a photoactive layer, wherein the photoactive layer includes an electron donor and an electron acceptor, the electron donor includes a polymer including a first unit represented by Chemical Formula 1; a second unit represented by Chemical Formula 2; and a third unit represented by Chemical Formula 3, and the electron acceptor includes a non-fullerene-based compound.

Cross Reference to Related Applications

This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/KR2018/006836, filed Jun. 18, 2018, which claims priority from Korean Patent Application Nos. 10-2017-0079709, filed Jun. 23, 2017, the contents of which are incorporated herein in their entireties by reference. The above-referenced PCT International Application was published in the Korean language as International Publication No. WO 2019/236101 A1 on Dec. 27, 2018.

TECHNICAL FIELD

This application claims priority to and the benefits of Korean Patent Application No. 10-2017-0079709, filed with the Korean Intellectual Property Office on Jun. 23, 2017, the entire contents of which are incorporated herein by reference.

The present specification relates to an organic solar cell.

BACKGROUND ART

An organic solar cell is a device capable of directly converting solar energy to electric energy by applying a photovoltaic effect. Solar cells are divided into inorganic solar cells and organic solar cells depending on the materials forming a thin film and since existing inorganic solar cells already have limits in economic feasibility and material supplies, organic solar cells that are readily processed, inexpensive and have various functions have been highly favored as a long-term alternative energy source.

For solar cells, it is important to increase efficiency so as to output as much electric energy as possible from solar energy, and fullerene-based compounds, an existing electron acceptor material, have problems such as having a low absorption rate in a visible region and having low thermal stability.

Accordingly, many examples of an organic solar cell using non-fullerene-based compounds as an electron acceptor material have been reported, and power conversion efficiency thereof has reached approximately 4% to 5.9%. However, non-fullerene-based compounds exhibit favorable efficiency only in combination with specific polymers at present, and therefore, finding novel polymers capable of exhibiting favorable efficiency with non-fullerene-based compounds have been an important challenge.

DISCLOSURE Technical Problem

The present specification is directed to providing an organic solar cell.

Technical Solution

One embodiment of the present specification provides an organic solar cell including a first electrode; a second electrode disposed opposite to the first electrode; and one or more organic material layers disposed between the first electrode and the second electrode and including a photoactive layer, wherein the photoactive layer includes an electron donor and an electron acceptor, the electron donor includes a polymer including a first unit represented by the following Chemical Formula 1; a second unit represented by the following Chemical Formula 2; and a third unit represented by the following Chemical Formula 3, and the electron acceptor includes a non-fullerene-based compound.

In Chemical Formulae 1 to 3,

X1 to X5 are the same as or different from each other, and each independently selected from the group consisting of CR′, NR, O, SiRR′, PR, S, GeRR′, Se and Te,

Y1 to Y4 are the same as or different from each other, and each independently selected from the group consisting of CR″, N, SIR″, P and GeR″,

R, R′, R″, Q1 to Q4, R1 to R4, R10 and R11 are the same as or different from each other, and each independently hydrogen; deuterium; a halogen group; a hydroxyl group; a substituted or unsubstituted alkyl group; a substituted or unsubstituted cycloalkyl group; a substituted or unsubstituted alkoxy group; a substituted or unsubstituted aryloxy group; a substituted or unsubstituted alkenyl group; a substituted or unsubstituted amine group; a substituted or unsubstituted aryl group; or a substituted or unsubstituted heterocyclic group,

R20 and R21 are the same as or different from each other, and each independently a substituted or unsubstituted alkoxy group; or a substituted or unsubstituted aryloxy group,

a, b, d and e are each an integer of 0 to 3,

when a b, d or e is 2 or greater, structures in the two or more parentheses are the sane as or different from each other, and

A1 to A4 are the same as or different from each other, and each independently hydrogen, fluorine or chlorine, and at least one of A1 to A4 is fluorine or chlorine.

Advantageous Effects

An organic solar cell according to one embodiment of the present specification uses the polymer as an electron donor, and uses the non-fullerene-based compound as an electron acceptor, and thereby has excellent thermal stability and power conversion efficiency.

In addition the polymer according to one embodiment of the present specification has a high HOMO energy level, and therefore, the organic solar cell including this polymer as an electron donor of a photoactive layer has an excellent open circuit voltage property.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an organic solar cell according to one embodiment of the present specification.

FIG. 2 is a diagram presenting a UV-vis absorption spectrum of Polymer 1.

FIG. 3 is a diagram presenting voltage-dependent current density of an organic solar cell of Example 2.

FIG. 4 is a diagram presenting voltage-dependent current density of organic solar cells of Comparative Examples 1 and 2.

FIG. 5 is a diagram presenting an NMR spectrum of Chemical Formula K synthesized in a preparation example.

FIG. 6 is a diagram presenting an NMR spectrum of Chemical Formula K-1 synthesized in a preparation example.

REFERENCE NUMERAL

-   -   101: Anode (ITO)     -   102: Hole Transfer Layer (PEDOT:PSS)     -   103: Photoactive Layer     -   104: Cathode (Al)

Mode for Disclosure

Hereinafter, the present specification will be described in more detail.

In the present specification, a ‘unit’ is a repeated structure included in a monomer of a polymer, and means a structure in which the monomer bonds in the polymer by polymerization.

In the present specification, the meaning of ‘including a unit’ means being included in a main chain in a polymer.

In the present specification, a description of a certain part ‘including’ certain constituents means capable of further including other constituents, and does not exclude other constituents unless particularly stated on the contrary.

In the present specification, a description of one member being placed ‘on’ another member includes not only a case of the one member adjoining the another member but a case of still another member being present between the two members.

In the present specification, an energy level means magnitude of energy. Accordingly, even when an energy level is expressed in a negative (−) direction from a vacuum level, the energy level is interpreted to mean an absolute value of the corresponding energy value. For example, a HOMO energy level means a distance from a vacuum level to a highest occupied molecular orbital. In addition, a LUMO energy level means a distance from a vacuum level to a lowest unoccupied molecular orbital.

One embodiment of the present specification provides an organic solar cell including a first electrode; a second electrode disposed opposite to the first electrode; and one or more organic material layers disposed between the first electrode and the second electrode and including a photoactive layer, wherein the photoactive layer includes an electron donor and an electron acceptor, the electron donor includes a polymer including a first unit represented by Chemical Formula 1; a second unit represented by Chemical Formula 2; and a third unit represented by Chemical Formula 3, and the electron acceptor includes a non-fullerene-based compound.

In a photoactive layer of an organic solar cell, an electron donor and an electron acceptor absorb light to form excitons, and the produced excitons migrate to an interface of the electron donor and electron acceptor, and are separated into electrons and holes. The electrons migrate along the electron acceptor and the holes migrate along the electron donor to each electrode to produce a current. Herein, how well morphology of the electron donor and the electron acceptor is electrically formed has decisive effects on current generation, and the polymer forms morphology particularly well with non-fullerene-based compounds ultimately enhancing efficiency of an organic solar cell.

Examples of the substituents are described below, however, the substituents are not limited thereto.

The term “substitution” means a hydrogen atom bonding to a carbon atom of a compound is changed to another substituent and the position of substitution is not limited as long as it is a position at which the hydrogen atom is substituted, that is, a position at which a substituent can substitute, and when two or more substituents substitute, the two or more substituents may be the same as or different from each other.

The term “substituted or unsubstituted” in the present specification means being substituted with one or more substituents selected from the group consisting of deuterium; a halogen group; a nitrile group; a nitro group; a hydroxyl group; a substituted or unsubstituted alkyl group; a substituted or unsubstituted cycloalkyl group; a substituted or unsubstituted alkoxy group; a substituted or unsubstituted aryloxy group; a substituted or unsubstituted alkenyl group; a substituted or unsubstituted aryl group; and a substituted or unsubstituted heterocyclic group, or being substituted with a substituent linking two or more substituents among the substituents illustrated above, or having no substituents. For example, “a substituent linking two or more substituents” may, include a biphenyl group. In other words, a biphenyl group may be an aryl group, or interpreted as a substituent linking two phenyl groups.

In the present specification examples of the halogen group include fluorine, chlorine, bromine or iodine.

In the present specification, the alkyl group may be linear or branched, and although not particularly limited thereto, the number of carbon atoms is preferably from 1 to 50. Specific examples thereof may include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-buyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-penlyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, cyclopentylmethyl, cyclohexylmethyl, cyclohexyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylhexyl, 4-methylhexyl, 5-methylhexyl and the like, but are not limited thereto.

In the present specification, the cycloalkyl group is not particularly limited, but preferably has 3 to 60 carbon atoms, and specific examples thereof may include cyclopropyl, cyclobutyl, cyclopentyl, 3-methylcyclopentyl, 2,3-dimethylcyclopentyl, cyclohexyl, 3-methylcyclohexyl, 4-methylcyclohexyl, 2,3-dimethylcyclohexyl, 3,4,5-trimethylcyclohexyl, 4-tert-butylcyclohexyl, cycloheptyl, cyclooctyl and the like, but are not limited thereto.

In the present specification, the alkoxy group may be linear, branched or cyclic. The number of carbon atoms of the alkoxy group is not particularly limited, but is preferably from 1 to 20. Specific examples thereof may include methoxy, ethoxy, n-propoxy, isopropoxy, i-propyloxy, n-butoxy, isobutoxy, tert-butoxy, sec-butoxy, n-pentyloxy, neopentyloxy, isopentyloxy, n-hexyloxy, 3,3-dimethylbutyloxy, 2-ethylbutyloxy, n-octyloxy n-nonyloxy, n-decyloxy, benzyloxy, p-methylbenzyloxy and the like, but are not limited thereto.

In the present specification, the alkenyl group may be linear or branched, and although not particularly limited thereto, the number of carbon atoms is preferably from 2 to 40. Specific examples thereof may include vinyl, 1-propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl 2-pentenyl, 3-pentenyl, 3-methyl-1-butenyl, 1,3-butadienyl, allyl, 1-phenylvinyl-1-yl, 2-phenylvinyl-1-yl, 2,2-diphenylvinyl-1-yl, 2-phenyl-2-(naphthyl-1-yl)vinyl-1-yl, 2,2-bis(diphenyl-1-yl)vinyl-1-yl, a stilbenyl group, a styrenyl group and the like, but are not limited thereto.

In the present specification, the number of carbon atoms of the amine group is not particularly limited, but is preferably from 1 to 30. In the amine group, the N atom may be substituted with an aryl group, an alkyl group, an arylalkyl group, a heterocyclic group and the like, and specific examples of the amine group may include a methylamine group, a dimethylamine group, an ethylamine group, a diethylamine group, a phenylamine group, a naphthylamine group, a biphenylamine group, an anthracenrylamine group, a 9-methyl-anthracenylamine group, a diphenylamine group, a phenylnaphthylamine group, a ditolylamine group, a phenyholylamine group, a triphenylamine group and the like, but are not limited thereto.

In the present specification, when the aryl group is a monocyclic aryl group, the number of carbon atoms is not particularly limited, but is preferably from 6 to 25. Specific examples of the monocyclic aryl group may include a phenyl group, a biphenyl group, a terphenyl group and the like, but are not limited thereto.

In the present specification, when the aryl group is a polycyclic aryl group, the number of carbon atoms is not particularly limited, but is preferably from 10 to 24. Specific examples of the polycyclic aryl group may include a naphthyl group, an anthracenyl group, a phenanthryl group, a pyrenyl group, a perylenyl group, a chrysenyl group, a fluorenyl group and the like, but are not limited thereto.

In the present specification, the fluorenyl group may be substituted, and adjacent substituents may bond to each other to form a ring.

In the present specification, the arylene group means the aryl group having two bonding sites, that is, a divalent group. Descriptions on the aryl group provided above may be applied thereto except for these each being divalent.

In the present specification, the heterocyclic group is a group including one or more atoms that are not carbon, that is, heteroatoms, and specifically, the heteroatom may include one or more atoms selected from the group consisting of O, N, Se, S and the like. The number of carbon atoms of the heterocyclic group is not particularly limited, but is preferably from 2 to 60. Examples of the heterocyclic group may include a thiophene group, a furan group, a pyrrole group, an imidazole group, a thiazole group, an oxazole group, an oxadiazole group, a triazole group, a pyridyl group, a bipyridyl group, a pyrimidyl group, a triazine group, a triazole group, an acridyl group, a pyridazine group, a pyrazinyl group, a quinolinyl group, a quinazoline group, a quinoxalinyl group, an isoquinoline group, an indole group, a carbazole group, a benzoxazole group, a benzimidazole group, a benzothiazole group, a benzocarbazole group, a benzothiophene group, a dibenzothiophene group, a benzofuranyl group, a phenanthroline group, a thiazolyl group, an isoxazolyl group, an oxadiazolyl group, a thiadiazolyl group, a phenothiazinyl group, a dibenzofuranyl group and the like, but are not limited thereto.

In the present specification, the aryl group of the aryloxy group is the same as the examples of the aryl group described above. Specific examples of the aryloxy group may include phenoxy, p-tolyloxy, m-tolyloxy, 3,5-dimethyl-phenoxy, 2,4,6-trimethylphenoxy, p-tert-butylphenoxy, 3-biphenyloxy, 4-biphenyloxy, 1-naphthyloxy, 2-naphthyloxy, 4-methyl-1-naphthyloxy, 5-methyl-2-naphthyloxy, 1-anthryloxy, 2-anthryloxy, 9-anthryloxy, 1-phenanthryloxy, 3-phenanthryloxy, 9-phenanthryloxy and the like, but are not limited thereto.

In one embodiment of the present specification, the non-fullerene-based compound may be represented by the following Chemical Formula A.

In Chemical Formula A,

Ra to Rf are the same as or different from each other, and each independently hydrogen; or a substituted or unsubstituted alkyl group,

La to Ld are the same as or different from each other, and each independently a substituted or unsubstituted arylene group; or a substituted or unsubstituted divalent heterocyclic group,

Ma and Mb are the same as or different from each other, and each independently hydrogen; a halogen group; or a substituted or unsubstituted alkyl group,

p and q are each independently an integer of 0 to 2, and

when p or q is 2, structures in the parentheses are the same as each other.

In one embodiment of the present specification, Ra to Rd are each an alkyl group.

In another embodiment, Ra to Rd are each an alkyl group having 1 to 30 carbon atoms.

In another embodiment, Ra to Rd are each an alkyl group having 1 to 10 carbon atoms.

In one embodiment of the present specification, Re and Rf are hydrogen.

In one embodiment of the present specification, La to Ld are each an arylene group.

In another embodiment, La to Ld are each an arylene group having 6 to 25 carbon atoms.

In another embodiment, La to Ld are a phenylene group.

In another embodiment, La to Ld are each a divalent heterocyclic group.

In another embodiment, La to Ld are each a divalent heterocyclic group having 2 to 30 carbon atoms.

In another embodiment, La to Ld are each a divalent heterocyclic group having 2 to 10 carbon atoms.

In another embodiment, La to Ld are a divalent thiophene group.

In one embodiment of the present specification, Ma and Mb are hydrogen.

In another embodiment, Ma and Mb are each an alkyl group.

In another embodiment. Ma and Mb are each an alkyl group having 1 to 10 carbon atoms.

In another embodiment, Ma and Mb are a methyl group.

In another embodiment Ma and Mb are each a halogen group.

In another embodiment, Ma and Mb are fluorine.

In one embodiment of the present specification, p and q are 0.

In another embodiment, p and q are 1.

In another embodiment, p and q are 2.

In addition, in one embodiment of the present specification, the compound represented by Chemical Formula A may be any one of the following Chemical Formulae A-1 to A-5.

In present specification, Me means a methyl group.

In one embodiment of the present specification, the non-fullerene-based compound has higher thermal stability compared to fullerene-based compounds.

In addition, in one embodiment of the present specification, an organic solar cell including the non-fullerene-based compound as an electron acceptor of a photoactive layer and including the polymer as an electron donor of a photoactive layer has excellent thermal stability and has excellent power conversion efficiency.

The polymer according to one embodiment of the present specification includes the first unit represented by Chemical Formula 1.

In one embodiment of the present specification, two groups of A1 to A4 are fluorine or chlorine, and may substitute at a position opposite to each other in the benzene ring, that is, a para position. In this case, fluorine or chlorine of the first unit interacts with an S atom of thiophene of the first unit, or interacts with X1 and/or X2 of the second unit to increase planarity of the polymer.

In the present specification, the interaction means a chemical structure or atoms forming the chemical structure having non-covalent interactions affected by each other through actions other than covalent bonding, and for example, may mean chalcogen bonding.

The polymer according to one embodiment of the present specification may have its planarity enhanced by minimizing a torsion angle of a backbone of the polymer through non-covalent interactions within the unit or with other neighboring units. In addition, non-covalent interactions enhance π-π stacking, and thereby enhance charge mobility due to delocalization of polarons and excitons, which is effective in packing.

Accordingly, including the polymer according to one embodiment of the present specification may induce an increase in the fill factor (FF), and a device with high efficiency may be provided.

In one embodiment of the present specification, A1 to A4 are the same as or different from each other and each independently hydrogen, fluorine or chlorine, and at least one of A1 to A4 is fluorine or chlorine.

In one embodiment of the present specification, at least one of A1 to A4 is fluorine.

In one embodiment of the present specification, two groups of A1 to A4 are fluorine or chlorine, and the two groups may be present at a para position to each other with respect to the benzene ring.

In one embodiment of the present specification, A1 and A4 are each fluorine or chlorine, and A2 and A3 are hydrogen.

In one embodiment of the present specification, A2 and A3 are each fluorine or chlorine, and A1 and A4 are hydrogen.

In one embodiment of the present specification, a is an integer of 1 to 3.

In another embodiment, a is 1.

In one embodiment of the present specification, b is an integer of 1 to 3.

In another embodiment, b is 1.

In one embodiment of the present specification, R1 to R4 are hydrogen.

The polymer according to one embodiment of the present specification includes the second unit represented by Chemical Formula 2.

In one embodiment of the present specification, X1 is S.

In addition, in one embodiment of the present specification, X2 is S.

In one embodiment of the present specification, Y1 is CR″.

In addition, in one embodiment of the present specification, Y2 is CR″.

In one embodiment of the present specification, R″ is a substituted or unsubstituted heterocyclic group.

In addition, in one embodiment of the present specification, R″ is a substituted or unsubstituted thiophene group.

In one embodiment of the present specification, the second unit represented by Chemical Formula 2 is represented by the following Chemical Formula 2-1.

In Chemical Formula 2-1,

R12 and R13 are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group; a substituted or unsubstituted alkoxy group; a substituted or unsubstituted aryl group; or a substituted or unsubstituted heterocyclic group.

In one embodiment of the present specification, R12 and R13 are the same as or different from each other, and each independently a substituted or unsubstituted heterocyclic group.

In addition, in one embodiment of the present specification, R12 and R13 are the same as or different from each other, and each independently a substituted or unsubstituted heterocyclic group including one or more S atoms.

In one embodiment of the present specification, R12 is a thiophene group.

In addition, in one embodiment of the present specification, R13 is a thiophene group.

In one embodiment of the present specification, the second unit represented by Chemical Formula 2 is represented by the following Chemical Formula 2-2.

In Chemical Formula 2-2,

R14 and R15 are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group: or a substituted or unsubstituted alkoxy group.

In another embodiment, R14 and R15 are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

In another embodiment, R14 and R15 are the same as or different from each other, and each independently a substituted or unsubstituted 2-ethylhexyl group.

In one embodiment of the present specification, R14 and R15 are a 2-ethylhexyl group.

The polymer according to one embodiment of the present specification includes the third unit represented by Chemical Formula 3.

In one embodiment of the present specification, X3 is S.

In another embodiment, X4 is S.

In one embodiment of the present specification, X5 is S.

In one embodiment of the present specification, Y3 is N.

In another embodiment, Y4 is N.

In another embodiment, d is 0.

In another embodiment, d is 1.

In one embodiment of the present specification, e is 1.

In another embodiment, e is 0.

In one embodiment of the present specification, Q1 to Q4 are hydrogen.

In one embodiment of the present specification, R20 and R21 are the same as or different from each other, and each independently a substituted or unsubstituted alkoxy group.

In one embodiment of the present specification, the third unit represented by Chemical Formula 3 is represented by the following Chemical Formula 3-1 or Chemical Formula 3-2.

In Chemical Formula 3-1 and Chemical Formula 3-2,

R20 and R21 have the same definitions as in Chemical Formula 3.

In one embodiment of the present specification, R20 and R21 are the same as or different from each other, and each independently a substituted or unsubstituted alkoxy group.

In another embodiment, R20 and R21 are the same as or different from each other and each independently a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

In another embodiment, R20 and R21 are the same as or different from each other, and each independently a substituted or unsubstituted dodecyloxy group.

In one embodiment of the present specification, R20 and R21 are a dodecyloxy group.

In one embodiment of the present specification, the polymer includes a unit represented by the following Chemical Formula 4.

[Chemical Formula 4]

In Chemical Formula 4,

l is, as a mole fraction, a real number of 0<l<1,

m is, as a mole fraction, a real number of 0<m<1,

A is the first unit represented by Chemical Formula 1,

B is the second unit represented by Chemical Formula 2,

C and C′ are the same as or different from each other, and each independently the third unit represented by Chemical Formula 3, and

n is, as a unit repetition number, an integer of 1 to 10,000.

In one embodiment of the present specification, A of Chemical Formula 4 is the first unit represented by Chemical Formula 1, and a and b are each independently an integer of 1 to 3.

In addition, in one embodiment of the present specification, A of Chemical Formula 4 is the first unit represented by Chemical Formula 1, and a and b are 1.

In one embodiment of the present specification, B of Chemical Formula 4 is the second unit represented by Chemical Formula 2-2.

In one embodiment of the present specification, C and C′ of Chemical Formula 4 are the third unit represented by Chemical Formula 3-1.

In addition, by the third unit represented by Chemical Formula 3 including R20 and R21 in one embodiment of the present specification, an O atom of R20 and R21; fluorine or chlorine of the first unit represented by Chemical Formula 1; and an S atom of the second unit represented by Chemical Formula 2 may form a planar structure through interactions with each other.

In one embodiment of the present specification, the polymer includes a unit represented by the following Chemical Formula 5.

In Chemical Formula 5,

R27 to R30 are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group; or a substituted or unsubstituted a yl group,

R31 to R42 are the same as or different from each other, and each independently hydrogen; or a substituted or unsubstituted alkyl group,

A1 and A4 have the same definitions as in Chemical Formula 1,

l is, as a mole fraction, a real number of 0<l<1,

m is, as a mole fraction, a real number of 0<m<1,

l+m==1, and

n is, as a unit repetition number, an integer of 1 to 10,000.

In one embodiment of the present specification, R27 to R30 are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group.

In another embodiment, R27 to R30 are the same as or different from each other, and each independently an alkyl group having 1 to 15 carbon atoms.

In one embodiment of the present specification, R31 is a substituted or unsubstituted alkyl group having 1 to 15 carbon atoms.

In one embodiment of the present specification, R32 to 137 are hydrogen.

In one embodiment of the present specification, R38 is a substituted or unsubstituted alkyl group having 1 to 15 carbon atoms.

In one embodiment of the present specification, R39 to R42 are hydrogen.

In one embodiment of the present specification, A1 and A4 are fluorine.

In one embodiment of the present specification, l is 0.5.

In another embodiment, m is 0.5.

In one embodiment of the present specification, the polymer includes a unit represented by the following Chemical Formula 5-1.

In one embodiment of the present specification, the polymer includes a unit represented by the following Chemical Formula 6 or 7.

In Chemical Formulae 5-1, 6 and 7, l, m and n have the same definitions as in Chemical Formula 5.

In one embodiment of the present specification, the polymer is a random polymer. When the polymer is a random polymer, solubility is enhanced, which is economically effective cost-wise in terms of a device manufacturing process.

In one embodiment of the present specification, an end group of the polymer is a substituted or unsubstituted heterocyclic group; or a substituted or unsubstituted aryl group.

In one embodiment of the present specification, an end group of the polymer is a 4-(trifluoromethyl)phenyl group.

In one embodiment of the present specification, an end group of the polymer is a bromo-thiophene group.

In another embodiment, an end group of the polymer is a trifluoro-benzene group.

In one embodiment of the present specification, the electron donor is a polymer including the first unit represented by Chemical Formula 1; the second unit represented by Chemical Formula 2; and the third unit represented by Chemical Formula 3, and the electron acceptor is a non-fullerene-based compound.

In another embodiment, the electron donor is a polymer including the unit represented by Chemical Formula 5, and the electron acceptor is the compound represented by Chemical Formula A.

In one embodiment of the present specification, the electron donor and the electron acceptor have a mass ratio of 1:1 to 1:4. The ratio is preferably from 1:1.5 to 1:2.5, and more preferably from 1:1.8 to 1:2.2.

According to one embodiment of the present specification, the polymer preferably has a number average molecular weight of 5,000 g/mol to 1,000,000 g/mol.

According to one embodiment of the present specification, the polymer may have molecular weight distribution of 1 to 10. The polymer preferably has molecular weight distribution of 1 to 3.

Electrical properties and mechanical properties become better as the molecular weight distribution decreases and the number average molecular weight increases.

In addition, the number average molecular weight is preferably 100,000 g/mol or less so that a solution coating method is favorably used by having solubility of certain level or higher.

The polymer may be prepared by introducing monomers of each unit with Pd₂(dba)₃ and P(o-tolyl)₃ with chlorobenzene as a solvent, and polymerizing the result using a microwave reactor.

The polymer according to the present specification may be prepared through a multi-step chemical reaction. After preparing monomers through an alkylation reaction, a Grignard reaction, a Suzuki coupling reaction, a Stille coupling reaction and the like, final polymers may be prepared through a carbon-carbon coupling reaction such as a Stille coupling reaction. When a substituent to introduce is a boronic acid or boronic ester compound, the polymer may be prepared through a Suzuki coupling reaction, and when a substituent to introduce is a tributyltin or trimethyltin compound, the polymer may be prepared through a Stille coupling reaction, however, the preparation is not limited thereto.

An organic solar cell according to one embodiment of the present specification includes a first electrode, a photoactive layer and a second electrode, the organic solar cell may further include a substrate, a hole transfer layer and/or an electron transfer layer.

In one embodiment of the present specification, when the organic solar cell receives photons from an external light source, electrons and holes are generated between an electron donor and an electron acceptor. The generated holes are transferred to an anode through an electron donor layer.

FIG. 1 is a diagram illustrating an organic solar cell according to one embodiment of the present specification including an anode (101), a hole transfer layer (102), a photoactive layer (103) and a cathode (104).

In one embodiment of the present specification, the organic solar cell may further include additional organic material layers. The organic solar cell may reduce the number of organic material layers by using organic materials having various functions at the same time.

In one embodiment of the present specification in the organic solar cell, the layers may be arranged in the order of a cathode, a photoactive layer and an anode, or may also be arranged in the order of an anode, a photoactive layer and a cathode, however, the disposition is not limited thereto.

In another embodiment, in the organic solar cell, the layers may be arranged in the order of an anode, a hole transfer layer, a photoactive layer, an electron transfer layer and a cathode, or may also be arranged in the order of a cathode, an electron transfer layer, a photoactive layer, a hole transfer layer and an anode, however, the disposition is not limited thereto.

In one embodiment of the present specification, the organic solar cell has a normal structure. In the normal structure, the layers may be laminated in the order of a substrate, a first electrode, a hole transfer layer, an organic material layer including a photoactive layer, an electron transfer layer and a second electrode.

In one embodiment of the present specification, the organic solar cell has an inverted structure. In the inverted structure, the layers may be laminated in the order of a substrate, a first electrode, an electron transfer layer, an organic material layer including a photoactive layer, a hole transfer layer and a second electrode.

In one embodiment of the present specification, the first electrode is an anode, and the second electrode is a cathode. In another embodiment, the first electrode is a cathode, and the second electrode is an anode.

In one embodiment of the present specification, the organic solar cell has a tandem structure. In this case, the organic solar cell may include two or more layers of photoactive layers. The organic solar cell according to one embodiment of the present specification may have a photoactive layer in one, or two or more layers.

In another embodiment, a buffer layer may be disposed between a photoactive layer and a hole transfer layer, or between a photoactive layer and an electron transfer layer. Herein, a hole injection layer may be further disposed between an anode and the hole transfer layer. In addition, an electron injection layer may be further disposed between a cathode and the electron transfer layer.

In one embodiment of the present specification, the electron donor and the electron acceptor form a bulk heterojunction (BHJ).

A bulk heterojunction means an electron donor material and an electron acceptor material being mixed together in a photoactive layer.

In one embodiment of the present specification, the photoactive layer further includes an additive.

In one embodiment of the present specification, the additive has a molecular weight of 50 g/mol to 300 g/mol.

In another embodiment, the additive is an organic material having a boiling point of 30° C. to 300° C.

In the present specification, the organic material means a material including at least one or more carbon atoms.

In one embodiment, the additive may further include one or more types of additives among additives selected from the group consisting of 1,8-diiodooctane (DIO), 1-chloronaphthalene (1-CN), diphenyl ether (DPE), octanedithiol and tetrabromothiophene.

In one embodiment of the present specification, the photoactive layer has a bilayer structure including an n-type organic material layer and a p-type organic material layer, and the p-type organic material layer includes the polymer.

The substrate in the present specification may include a glass substrate or a transparent plastic substrate having excellent transparency, surface smoothness, handling easiness and water resistance, but is not limited thereto, and substrates typically used in organic solar cells may be used without limit. Specific examples thereof include glass, polyethylene terphthalate (PET), polyethylene naphthalate (PEN), polypropylene (PP), polyimide (PI), triacetyl cellulose (TAC) or the like, but are not limited thereto.

A material of the first electrode may include a material that is transparent and has excellent conductivity, however, the material is not limited thereto. Examples thereof may include metals such as vanadium chromium copper, zinc or gold, or alloys thereof metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO) or indium zinc oxide (IZO); combinations of metals and oxides such as ZnO:Al or SnO₂:Sb; conductive polymers such as poly(3-methylthiophene), poly[3,4-(ethylene-1,2-dioxy)thiophene] (PEDOT), polypyrrole or polyaniline, or the like, but are not limited thereto.

A method of forming the first electrode is not particularly limited, however, a method of, for example, sputtering, E-beam, thermal deposition spin coating, screen printing, inkjet printing, doctor blade or gravure printing may be used.

When forming the first electrode on a substrate, the result may go through processes of cleaning, dehydrating and modifying to be hydrophilic.

For example, after a patterned ITO substrate is cleaned with a cleaning agent, acetone and isopropyl alcohol (IPA) in consecutive order, the ITO substrate is dried for 1 minute to 30 minutes at 100° C. to 150° C., preferably for 10 minutes at 120° C., on a heating plate in order to dehydrate, and when the substrate is completely cleaned, the surface of the substrate is modified to be hydrophilic.

Through the surface modification such as above, the junctional surface potential may be maintained at a level suitable as surface potential of a photoactive layer. In addition, when a surface is modified, a polymer thin film may be readily formed on a first electrode, and the quality of the thin film may be improved.

Preprocessing technologies for the first electrode include a) a surface oxidation method using parallel plate discharge, b) a method of oxidizing the surface through ozone generated using UV rays in a vacuum state, and c) an oxidation method using oxygen radicals generated by plasma.

One of the methods described above may be selected depending on the condition of the first electrode or the substrate. However, it is commonly preferred to prevent the leave of oxygen on the surface of the first electrode or the substrate and to suppress the remaining of moisture and organic materials as much as possible, no matter which method is used. Practical effects of the preprocessing may be maximized in this case.

As a specific example, a method of oxidizing the surface through ozone generated using UV may be used. Herein, a patterned ITO substrate may be fully dried by baking the patterned ITO substrate on a hot plate after being ultrasonic cleaned, and the patterned ITO substrate is introduced into a chamber and then may be cleaned by the ozone generated by reacting oxygen gas with UI light using a UV lamp.

However, the method of surface modification of the patterned ITO substrate in the present specification is not particularly limited, and any method oxidizing a substrate may be used.

The second electrode may include a metal having small work function, but is not limited thereto. Specific examples thereof may include any one of metals such as magnesium calcium, sodium, potassium, titanium indium, yttrium, lithium, gadolinium, aluminum, silver, tin and lead, or alloys thereof; and multilayer-structured materials such as LiF/Al, LiO₂/Al, LiF/Fe, Al:Li, Al:BaF₂ and Al:BaF₂:Ba, but are not limited thereto.

The second electrode may be formed by being deposited inside a thermal depositor having a vacuum degree of 5×10⁻⁷ torr or less, however, the formation is not limited to this method.

The hole transfer layer and/or the electron transfer layer play a role of efficiently transferring the electrons and the holes separated in a photoactive layer to an electrode, and the material is not particularly limited.

The hole transfer layer material may include poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS), molybdenum oxide (MoO_(x)); vanadium oxide (V₂O₅); nickel oxide (NiO); tungsten oxide (WO_(x)) and the like, but is not limited thereto.

The electron transfer layer material may include electron-extracting metal oxides, and may specifically include a metal complex of 8-hydroxyquinoline; a complex including Alq₃; a metal complex including Liq; LiF; Ca; titanium oxide (TiO_(x)); zinc oxide (ZnO); cesium carbonate (Cs₂CO₃), and the like, but is not limited thereto.

The photoactive layer may be formed by dissolving a photoactive material such as an electron donor and/or an electron acceptor in an organic solvent, and then applying the solution using a method such as spin coating, dip coating, screen printing, spray coating, doctor blade or brush painting, however, the method is not limited thereto.

Hereinafter, the present specification will be described in detail with reference to examples in order to specifically describe the present specification. However, examples according to the present specification may be modified to various different forms, and the scope of the present specification is not construed as being limited to the examples described below. The examples of the present specification are provided in order to more fully describe the present specification to those having average knowledge in the art.

Preparation Example: Synthesis of Polymer 1

(1) Synthesis of Chemical Formula K

After introducing toluene to two starting materials and adding 0.05 equivalents of tetrakis(triphenylphosphine)palladium(0) (Pd(PPh₃)₄) thereto, the result was stirred for 15 hours at 80° C., and the reaction solution gradually changed to black. This was worked up, dried with magnesium sulfate, and then recrystallized to obtain Chemical Formula K (white powder, 4.3 g).

An NMR spectrum of the synthesized Chemical Formula K is presented in FIG. 5 .

(2) Synthesis of Chemical Formula K-1

After dissolving the prepared Chemical Formula K in tetrahydrofuran (THF) and lowering the temperature to −78° C., 2.1 equivalents of n-butyllithium (n-BuLi) was added thereto, and the result was stirred for 30 minutes. After that, the result was further stirred for 1 hour at room temperature, and the solution color changed to yellow. The temperature was lowered to −78° C. again 2.1 equivalents of trimethyltin chloride was added thereto, and the result was stirred for 12 hours while slowly raising the temperature to room temperature. After 12 hours, the solution color changed to ocher, and when crystallizing the result after work up, Chemical Formula K-1 in a glossy plate-type yellow solid form was obtained.

An NMR spectrum of the synthesized Chemical Formula K-1 is presented in FIG. 6 ,

(3) Synthesis of Chemical Formula L

A compound of Chemical Formula L was synthesized based on JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2011, 49, 4387-4397, 4389.

(4) Synthesis of Chemical Formula M

After introducing and dissolving 2-(2-ethylhexyl)thiophene (10.0 g, 59.4 mmol) in 500 ml of tetrahydrofuran (THF), the temperature was lowered to −78° C. At this temperature, 2.5 M n-butyllithium (n-BuLi) dissolved in hexane (24.0 ml, 59.4 mmol) was slowly added thereto, and the result was stirred for 30 minutes. After that, the temperature was raised up to 0° C., and after stirring the result for 1 hour in this state, 4,8-dihydrobenzo[1,2-b:4,5-b′]dithiophene-4,8-dione (3.3 g, 14.8 mmol) was introduced thereto at once, and the result was stirred for 3 hours 50° C. After lowering the temperature of this solution to room temperature, tin(II)chloride dehydrate (26 g) and 1 M 1-HCl (56 ml) were added thereto, and the result was further stirred for 3 hours. Ice was poured into this solution, and the result was extracted twice with diethyl ether and washed twice with water, and residual water was removed using magnesium sulfate (MgSO₄). With the remaining solution, the solvent was removed under decompression, and Chemical Formula M in a yellow high density liquid form was obtained through silica column. (Yield: 64%)

(5) Synthesis of Chemical Formula M-1

After introducing and dissolving the compound of Chemical Formula M (3.9 g, 7.59 mmol) in 100 ml of tetrahydrofuran (THF), the temperature was lowered to 0°C. At this temperature, 1.6 M n-butyllithium (n-BuLi) dissolved in hexane (10.4 ml, 16.7 mmol) was slowly added thereto, and the result was stirred for 1 hour at room temperature. To this solution, 1 M trimethyltin chloride dissolved in THF (22.7 ml, 22.7 mmol) was introduced thereto at once, and the result was stirred for 2 hours. Water was poured into this solution, and the result was extracted twice with diethyl ether and washed twice with water, and residual water was removed using magnesium sulfate (MgSO₄). With the remaining solution, the solvent was removed under decompression, and the result was recrystallized with ethanol to obtain Chemical Formula M-1 in a light yellow crystalline form. (Yield: 87%)

(6) Synthesis of Polymer 1

The following Polymer 1 was prepared by, with chlorobenzene as a solvent, introducing the monomers of Chemical Formulae K-1, L and M-1 synthesized above with Pd₂(dba)₃ and P(o-tolyl)₃, and polymerizing the result using a microwave reactor.

[Polymer 1]

FIG. 2 is a diagram presenting a UV-vis absorption spectrum of Polymer 1.

Example: Manufacture of Organic Solar Cell Example 1

Polymer 1 and ITIC of Solarmer Materials Inc. were dissolved in 2 ml of chlorobenzene (CB) in a mass ratio of 1:2 to prepare a composite solution, and herein, a concentration of the composite solution was adjusted to 2.0 wt %,a and an organic solar cell employed a structure of ITO:PEDOT:PSS/photoactive layer/Al (anode/hole transfer layer/photoactive layer/cathode). A glass substrate coated with ITO in a bar-type of 1.5 cm×1.5 cm was ultrasonic cleaned using distilled water, acetone and 2-propanol, and after the ITO surface was ozone treated for 10 minutes, PEDOT:PSS (AI4083) was spin coated to a thickness of 45 nm, and the result was heat treated for 5 minutes at 235° C. For photoactive layer coating, the composite solution of Polymer 1 and ITIC was spin coated for 10 seconds at 1,300 rpm, and A1 was deposited to a thickness of 100 nm at a rate of 1 Å/s using a thermal evaporator under vacuum of 3×10⁻⁸ torr to manufacture an organic solar cell.

Example 2

An organic solar cell was manufactured in the same manner as in Example 1 except that the composite solution of Polymer 1 and ITIC was spin coated for 10 seconds at 1,500 rpm.

Example 3

An organic solar cell was manufactured in the same manner as in Example 1 except that the composite solution of Polymer 1 and ITIC was spin coated for 10 seconds at 1,700 rpm.

Comparative Example 1

An organic solar cell was manufactured in the same manner as in Example 1 except that a composite solution prepared by dissolving the following PTB7-Th and ITIC in 25 mg/ml of orthodichlorobenzene (ODCB) in a ratio of 1:1.3 was used instead of the composite solution of Polymer 1 and ITIC, and this was spin coated for 10 seconds at 1,200 rpm.

Comparative Example 2

An organic solar cell was manufactured in the same manner as in Comparative Example 1 except that the composite solution of PTB7-Th and ITIC was coated for 10 seconds at 1,500 rpm.

Comparative Example 3

An organic solar cell was manufactured in the same manner as in Example 1 except that a composite solution prepared by dissolving Polymer 1 and PC₆₁BM in a mass ratio of 1:2 and adjusting the concentration to 2.5 wt % was used instead of the composite solution of Polymer 1 and ITIC, and the spin coating rate was set at 1,000 rpm when forming the photoactive layer.

Comparative Example 4

An organic solar cell was manufactured in the same manner as in Comparative Example 3 except that the spin coating rate was set at 1,500 rpm when forming the photoactive layer.

Comparative Example 5

An organic solar cell was manufactured in the same manner as in Comparative Example 3 except that the spin coating rate was set at 2,000 rpm when forming the photoactive layer.

Photoelectric conversion properties of the organic solar cells manufactured in Examples 1 to 3 and Comparative Example 1 to Comparative Example 5 were measured under a 100 mW/cm² (AM 1.5) condition, and the results are shown in the following Table 1.

TABLE 1 J_(sc) PCE Photoactive Layer Voc (V) (mA/cm²) FF (%) Example 1 Polymer 1,300 0.919 13.607 0.620 7.75 1:ITIC = 1:2 rpm Example 2 1,500 0.920 13.378 0.644 7.92 rpm Example 3 1,700 0.916 13.026 0.526 6.28 rpm Comparative PTB7- 1,200 0.623 11.267 0.426 2.99 Example 1 Th:ITIC = 1:1.3 rpm Comparative 1,500 0.640 10.381 0.530 3.52 Example 2 rpm Comparative Polymer 1,000 0.758 5.210 0.566 2.21 Example 3 1:PC₆₁BM = 1:2 rpm Comparative 1,500 0.789 7.318 0.588 3.39 Example 4 rpm Comparative 2,000 0.792 7.002 0.588 3.26 Example 5 rpm

FIG. 3 is a diagram presenting voltage-dependent current density of the organic solar cell of Example 2, and FIG. 4 is a diagram presenting voltage-dependent current density of the organic solar cells of Comparative Examples 1 and 2. In Table 1, V_(oc) means an open circuit voltage, J_(sc) means a short-circuit current, FF means a fill factor, and PCE means energy conversion efficiency. The open circuit voltage and the short-circuit current are each an x-axis and a y-axis intercept in the four quadrants of a voltage-current density curve, and as these two values increase, solar cell efficiency is preferably enhanced. In addition, the fill factor is a value dividing the rectangle area that may be drawn inside the curve by the product of the short-circuit current and the open circuit voltage. The energy conversion efficiency may be obtained when these three values are divided by intensity of the irradiated light, and it is preferred as the value is higher.

In Table 1, it was seen that the organic solar cells of Examples 1 to 3 including Polymer 1 and ITIC in a photoactive layer had a higher open circuit voltage, had excellent device efficiency, and had excellent energy conversion efficiency compared to the organic solar cells of Comparative Examples 1 and 2 including PTB7-Th and ITIC in a photoactive layer.

In addition, it was identified that Examples 1 to 3 had far superior energy conversion efficiency compared to Comparative Examples 3 to 5, and based on this, it was seen that the polymer according to one embodiment of the present specification exhibited significantly superior performance when used together with a non-fullerene-based electron acceptor rather than a fullerene-based electron acceptor. 

What is claimed is:
 1. An organic solar cell comprising: a first electrode; a second electrode on the first electrode; and one or more organic material layers between the first electrode and the second electrode and including a photoactive layer, wherein the photoactive layer comprises an electron donor and an electron acceptor, the electron donor comprises a polymer comprising a first unit of Chemical Formula 1, a second unit of Chemical Formula 2, and a third unit of Chemical Formula 3:

wherein: X1 to X5 are the same as or different from each other, and each is independently selected from the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se and Te; Y1 to Y4 are the same as or different from each other, and each is independently selected from the group consisting of CR″, N, SiR″, P and GeR″; R, R′, R″, Q1 to Q4, R1 to R4, R10 and R11 are the same as or different from each other, and each is independently hydrogen, deuterium, a halogen group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted amine group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group; R20 and R21 are the same as or different from each other, and each is independently a substituted or unsubstituted alkoxy group, or a substituted or unsubstituted aryloxy group; a, b, d and e are each an integer of 0 to 3; when a, b, d or e is 2 or greater, structures in the two or more parentheses are the same as or different from each other; and A1 to A4 are the same as or different from each other, and each is independently hydrogen, fluorine or chlorine, and at least one of A1 to A4 is fluorine or chlorine, wherein the polymer comprises a unit of Chemical Formula 5:

wherein: R27 to R30 are the same as or different from each other, and each is independently a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; R31 to R42 are the same as or different from each other, and each is independently hydrogen, or a substituted or unsubstituted alkyl group; A1 and A4 have the same definitions as in Chemical Formula 1; l is, as a mole fraction, a real number of 0<l<1; m is, as a mole fraction, a real number of 0<m<1; l+m=1; and n is, as a unit repetition number, an integer of 1 to 10,000, and wherein the electron acceptor includes a non-fullerene-based compound of Chemical Formula A-1:


2. The organic solar cell of claim 1, wherein the second unit of Chemical Formula 2 is a unit of Chemical Formula 2-1:

wherein: R12 and R13 are the same as or different from each other, and each is independently a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group.
 3. The organic solar cell of claim 1, wherein the third unit of Chemical Formula 3 is a unit of Chemical Formula 3-1:

wherein: R20 and R21 have the same definitions as in Chemical Formula
 3. 4. The organic solar cell of claim 1, wherein the polymer comprises a unit of Chemical Formula 4: [Chemical Formula 4]

wherein: l is, as a mole fraction, a real number of 0<l<1; m is, as a mole fraction, a real number of 0<m<1; l+m=1; A is the first unit of Chemical Formula 1; B is the second unit of Chemical Formula 2; C and C′ are the same as or different from each other, and each is independently the third unit of Chemical Formula 3; and n is, as a unit repetition number, an integer of 1 to 10,000.
 5. The organic solar cell of claim 1, wherein the electron donor and the electron acceptor have a mass ratio of 1:1 to 1:4.
 6. The organic solar cell of claim 1, wherein the electron donor and the electron acceptor form a bulk heterojunction.
 7. The organic solar cell of claim 1, wherein the polymer is a random polymer.
 8. The organic solar cell of claim 1, wherein the polymer has a number average molecular weight of 5,000 g/mol to 1,000,000 g/mol.
 9. The organic solar cell of claim 1, wherein the polymer has molecular weight distribution of 1 to
 10. 10. The organic solar cell of claim 1, wherein the photoactive layer has a bilayer structure including an n-type organic material layer and a p-type organic material layer, and the p-type organic material layer includes the polymer.
 11. The organic solar cell of claim 1, wherein the second unit of Chemical Formula 2 is a unit of Chemical Formula 2-2:

wherein: R14 and R15 are the same as or different from each other, and each is independently a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group.
 12. The organic solar cell of claim 1, wherein the third unit of Chemical Formula 3 is a unit of Chemical Formula 3-2:

wherein: R20 and R21 have the same definitions as in Chemical Formula
 3. 13. The organic solar cell of claim 1, wherein the polymer comprises a unit of Chemical Formula 5-1, Chemical Formula 6, or Chemical Formula 7:

wherein: l, m and n have the same definitions as in Chemical Formula
 5. 14. The organic solar cell of claim 4, wherein l and m are each 0.5.
 15. The organic solar cell of claim 1, wherein l and m are each 0.5.
 16. The organic solar cell of claim 1, wherein the organic solar cell further comprises a substrate, a hole transfer layer and/or an electron transfer layer. 